The machine started to whine with any load on hydraulics. Changed filters and oil, no change. After running for 15-20 minutes the engine will occasionally lug and almost stall. The hydraulic piping will get hot and and alarm will sound. I'm thinking it may be a blockage of some type in the suction side or maybe pump. Any ideas were to look?
Sounds like your hydraulic system is going over relief. That's the whining that you are hearing. you may have a function dead headed or a failed relief valve. post your serial number and someone with knowledge of your machine can help you better.
There is a strainer basket in the hydraulic tank. Check it for being plugged with foreign material. Have you had any vandalism around where the machine is parked lately?
Serial Number: 11765
I have a Digital manual and a hydraulic pressure test set but don't know where to start checking.
Your machine is a 2000 year model. A suction side blockage won't over load the engine. There is a suction strainer in the tank. I don't know how to access it but on all the larger machine the fill cap is part of a plate held onto the tank with four bolts. If you removed the plate you will see what looks like a pipe with a spring in it. The strainer basket is at the bottom of that. You can pull up on it to remove the strainer. I haven't worked on a Dash 8 machine but most of the Komatsu minis use a piston pump and a gear pump piggy back. If there is a pump problem you would likely find brass of steel particles in the return filter and on the strainer basket. The hydraulic system in closed center load sensing hydraulics so it is possible that you have a problem on a load sense line or on a control valve on the pump itself. It is a pretty complicated system. I haven't been into any of those systems so can't tell you much except for generalities.
May have found the problem, While looking for issues that could cause the noise, I removed the air bleed bolt from the pump and no oil came out while engine was running. I just waited and finally oil began bubbling from pump. After a few minutes air stopped coming out and only oil. Sounds a lot quieter now.
So how did the air get in there? Check the strainer basket and the suction hose between the pump and the hydraulic reservoir.
Well, I may have spoken too soon. It is quieter and is quiet until you put a load on a tool. Just lifting the boom does not make it noisy. But as soon as you put a load on it, it will whine. No leaks on machine but I think I will pull strainer out of bottom of tank.